Electric motors are used with stators in environments with different pollution degrees. The higher the pollution degree is, the farther the current carrying components have to be removed from conductive components, so that no undesired discharge, i.e., short circuit, occurs. The spacing be maintained is determined here by the creepage and clearance distance, wherein, according to DIN VDE 0110-04.97, the clearance distance is defined as the shortest distance in air between two conductive parts, and the creepage distance is defined as the shortest distance along the surface of an insulating material between two conductive parts.
The creepage and clearance distances, particularly in the case of influence of pollution and humidity, must be much longer, so that the environmental air is not ionized by so-called pre-discharges and as a result breakdown can occur. No creepage or sliding discharges along the surface of the insulation material should occur.
In principle, if a stator is to be used in an environment with greater pollution (i.e., higher pollution degree), the creepage and clearance distance has to be longer. The values and spacings to be maintained here are defined by corresponding standard specifications. These standard specifications are determined depending on the requirements as well as the application fields and are established, for example, in the standards EN61800-5-1, EN60335-1, UL60730-1, UL1004-1 (-7) with reference to UL840.
However, in the dimensioning, one is subject to restrictions due to design, so that, in spite of the increase in the length of the creepage and clearance distances, the size of the stator cannot be increased for economic reasons. Here, moreover, the output, the torque and the degree of efficiency should also not become worse.
Therefore, in the prior art, slot closures are used in some cases, in which, however, the overlap has to be relatively large in order to ensure sufficient efficiency. The process is complicated and worsens the thermal factors.
Alternatively, the stator packet has been completely overmolded after the winding, so that it is protected from environmental influences and pollution. This process too is complicated and additionally cost intensive.
There are also solutions in the prior art in which the stator is coated entirely with powder coating material. However, here the stators first have to be cleaned, preheated, and subsequently vortex sintered or coated once or repeatedly. This process as well is very time and cost intensive.
Furthermore, in conventional stators, it is known to spray the grooves with plastic. Here, by increasing the groove opening width, more space for overmolding in the groove opening can be created, and the creepage and clearance distance can be increased. The groove opening is also referred to as “wiring trough” in the jargon of the field. However, this results in an undesired worsening of the motor cogging torque, which has a negative influence on noise generation.